MapReduce之输出结果排序

小灰灰 2022-04-23 17:04 291阅读 0赞

前面的案例中我们介绍了统计出每个用户的上行流量，下行流量及总流量，现在我们想要将输出的结果按照总流量倒序排序。

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9kcGItYm9ib2thb3lhLXNtLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70]

# 实现思路 #

MR程序在处理数据的过程中会对数据排序(map输出的kv对传输到reduce之前会排序)，排序的依据是map输出的key。所以我们如果要实现自己需要的排序规则，则可以考虑将排序因素放到key中，让key实现接口:WritableComparable,然后重写key的compareTo方法来指定比较规则

# 实现步骤 #

## 1.自定义Bean ##

import java.io.DataInput;
    import java.io.DataOutput;
    import java.io.IOException;
    
    import org.apache.hadoop.io.Writable;
    import org.apache.hadoop.io.WritableComparable;
    /** * 存储流量相关数据 * @author 波波烤鸭 * */
    public class Flow implements WritableComparable<Flow> { 
    	// 上下流量
    	private long upFlow;
    
    	// 下行流量
    	private long downFlow;
    	// 总流量
    	private long sumFlow;
    	
    	/** * 比较Flow对象的总流量 */
    	@Override
    	public int compareTo(Flow o) { 
    		// TODO Auto-generated method stub
    		return -(int)(this.sumFlow - o.getSumFlow());
    
    	}
    
    	public long getUpFlow() { 
    		return upFlow;
    	}
    
    	public void setUpFlow(long upFlow) { 
    		this.upFlow = upFlow;
    	}
    
    	public long getDownFlow() { 
    		return downFlow;
    	}
    
    	public void setDownFlow(long downFlow) { 
    		this.downFlow = downFlow;
    	}
    
    	public Flow(long upFlow, long downFlow) { 
    		super();
    		this.upFlow = upFlow;
    		this.downFlow = downFlow;
    		this.sumFlow = upFlow + downFlow;
    	}
    
    	/** * 无参构造方法必须要有 反射的时候需要用到 */
    	public Flow() { 
    		super();
    	}
    
    	/** * 序列化方法 */
    	@Override
    	public void write(DataOutput out) throws IOException { 
    		// TODO Auto-generated method stub
    		out.writeLong(upFlow);
    		out.writeLong(downFlow);
    		out.writeLong(sumFlow);
    	}
    
    	@Override
    	public String toString() { 
    		return upFlow + "\t" + downFlow + "\t" + sumFlow;
    	}
    
    	/** * 反序列化 反序列化的顺序和序列化的顺序一致 */
    	@Override
    	public void readFields(DataInput in) throws IOException { 
    		// TODO Auto-generated method stub
    		upFlow = in.readLong();
    		downFlow = in.readLong();
    		sumFlow = in.readLong();
    	}
    
    	public long getSumFlow() { 
    		return sumFlow;
    	}
    
    	public void setSumFlow(long sumFlow) { 
    		this.sumFlow = sumFlow;
    	}
    }

## 2.Map阶段 ##

public class FlowCountMap extends Mapper<LongWritable, Text, Flow, Text> { 
    
    	@Override
    	protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { 
    		// 将一行数据转换为String
    		String line = value.toString();
    		// 切分字段
    		String[] fields = line.split("\t");
    		// 取出手机号
    		String phoneNum = fields[0];
    		// 取出上行流量下行流量
    		long upFlow = Long.parseLong(fields[fields.length - 3]);
    		long downFlow = Long.parseLong(fields[fields.length - 2]);
    		Flow flow = new Flow(upFlow, downFlow);
    		context.write(flow, new Text(phoneNum));
    	}
    }

## 3.Reduce阶段 ##

public class FlowCountReducer extends Reducer<Flow, Text, Text, Flow>{ 
    
    	@Override
    	protected void reduce(Flow flow, Iterable<Text> values, Context context)
    			throws IOException, InterruptedException { 
    		
    		String phone = values.iterator().next().toString();
    		// 输出结果
    		context.write(new Text(phone), flow);
    	}
    }

## 4.启动类 ##

public static void main(String[] args) throws Exception { 
    		Configuration conf = new Configuration(true);
    		conf.set("mapreduce.framework.name", "local");
    		// 输出到HDFS文件系统中
    		// conf.set("fs.defaultFS", "hdfs://hadoop-node01:9000");
    		// 输出到本地文件系统
    		conf.set("fs.defaultFS", "file:///");
    		Job job = Job.getInstance(conf);
    		
    		job.setJarByClass(FlowTest.class);
    		
    		// 指定本job要使用的map/reduce的工具类
    		job.setMapperClass(FlowCountMap.class);
    		job.setReducerClass(FlowCountReducer.class);
    		
    		// 指定mapper输出kv的类型
    		job.setMapOutputKeyClass(Flow.class);
    		job.setMapOutputValueClass(Text.class);
    		
    		job.setOutputKeyClass(Text.class);
    		job.setOutputValueClass(Flow.class);
    		
    		// 指定job的原始文件输入目录
    		// 6.设置输出输出类
    		FileInputFormat.setInputPaths(job, new Path("c:/tools/bigdata/mr/sort/input/"));
    		FileOutputFormat.setOutputPath(job, new Path("c:/tools/bigdata/mr/sort/output/"));
    				
    		//将job中配置的相关参数，以及job所用的jar包提交给yarn运行
    		//job.submit(); waitForCompletion等待执行完成
    		boolean flag = job.waitForCompletion(true);
    		System.exit(flag?0:1);
    	}
    }

## 5.输出结果 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9kcGItYm9ib2thb3lhLXNtLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 1]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9kcGItYm9ib2thb3lhLXNtLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 2]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9kcGItYm9ib2thb3lhLXNtLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 3]

成功倒序输出  
本案例的目的有两个：

1.  实现对输出结果排序我们可以在自定义对象的compareTo方法中指定
2.  如果一次MapReduce任务获取不到我们需要的结果我们可以对输出的结果做多次MapReduce任务。

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